JP2018519990A - Multi-layer media floor filter with improved backwash - Google Patents

Abstract

In a multilayer media floor filter having a density that increases from the finest medium in the upper layer to the coarsest medium in the bottom layer, backwashing using air is performed without greatly destroying the layering of the media layer. When the air is stopped, the contaminants in the liquid above the finest medium removed by the air flow will flow either by the liquid injected above the medium or by the liquid flow passing through the medium without removing the finest medium. Is issued. The amount of contaminants remaining in the finest medium by air backwashing while maintaining stratification depends on whether the liquid backwash uses a flow rate sufficient to suspend the fine media or is below the suspension flow rate. Therefore, it is significantly less than when liquid backwashing is used alone.
[Selection] Figure 1

Description

Related cases

  This application claims priority from US Provisional Patent Application No. 62 / 169,807, filed June 2, 2015.

  The present invention relates to a method and apparatus for backwashing a multilayer media floor filter, and more particularly to a multilayer media floor filter with fine media.

  The multi-layer media floor filter is the applicant's international patent application, well known in the art, and is a known technique disclosed by WO 2014/012167 published on January 23, 2014. . The disclosure discloses various media beds for filtering fine particles, including configurations that use an upper layer of fine sand to improve the filtration function by providing appropriate flow characteristics at the media surface. Yes. As an advantage of such flow characteristics, it is possible to improve the function of collecting fine particles of a medium without clogging.

International Publication No. 2014/012167

  Such improved functionality creates a high need to remove trapped particulates and other contaminants during normal backwash. Before the function is reduced, it is more difficult to remove the contaminants in the fine sand by backwashing when the fine sand has a contaminant trapped deep inside the fine sand layer.

  In the conventional backwashing, in order to remove the contaminants collected by the filter and continuously filter the stock solution efficiently by the filter, the liquid flow is configured to be in the reverse direction of the filter. Liquid backwash typically fluidizes the media bed, transports filtered media particles and contaminants into suspension in the filter chamber, and media separation and liquid generation occurs prior to draining. Backwash flow is reduced, if possible, to reposition the filtration media and properly stratify.

  In the case of fine sand, it is difficult to separate contaminants from fine sand because small particles of the medium are retained in the suspension at relatively low flow rates. Under these conditions, such a flow is not very effective at removing contaminants from the media.

  It is known that the purification of the medium is performed using air. Air backwashing can purify more effectively than liquid backwashing. In this case, the liquid level on the medium can be reduced and air can be introduced through the medium layer by introducing air under the medium, thereby mixing the medium with the liquid on the medium bed. Can be pushed up. Subsequently, air flows out from the top of the filter reservoir while the liquid above the media bed is filled with a mixture of contaminants and media. The media in suspension is re-stratified to return to the normal media bed. This can be achieved by a controlled liquid flow through the suspending medium, which can constitute an arrangement of the media divided according to particle size. Liquid contaminants above the media bed can be drained.

  In the case of a fine sand filtration media bed, air backwash is a problem. Air can be used to efficiently wash the media, but the restratification achieved by using a controlled flow rate for larger particle size media suspends the fine sand. This is a problem because a remarkably low flow rate is used.

<Overview>
As used herein, the term “fine medium” refers to a fine filtration medium having an effective diameter of less than 0.4 mm, a minimum of about 0.2 mm, and preferably a minimum of 0.1 mm, the material being quartz sand, glass, plastic Quartz, gravel, metal, ceramic, etc. may be used. The effective diameter means that the above-mentioned medium may have a wide diameter, and the effective diameter may be an average diameter. For example, in the case of fine sand, particles having an average diameter of 0.22 mm will result in particles ranging from 0.12 mm to 0.35 mm. In the case of glass or polymer media, the particle size will be in a narrower range. Such a medium is effective in trapping fine contaminants in the range of 0.5 microns to 20 microns.

  Applicants have found that in multi-layer media floor filters with density increasing from fine media and top finest media to bottom coarsest media, efficient use of air without significantly breaking the media layer stratification Have found that it can be backwashed. By using air for backwashing, contaminants are removed from the fine media to the upper liquid level and contaminants around the fine media are also removed. When the air stops, the contaminants in the liquid above the fine medium removed by the air flow are flushed out by either the liquid injected above the medium or the liquid stream passing through the medium without removing the medium. Even if the amount of contaminants flowing out from the medium by air backwashing while maintaining stratification is at a flow rate sufficient to suspend the fine medium or below the limit flow rate, liquid backwashing is performed alone. More than in the case of

  Applicants have identified a media bed filter having a stock flow through a nozzle that creates a flow along the top surface of the media bed without overriding the media placement during a backwash wash cycle that efficiently removes contaminants from the media bed surface. It was further discovered that can be used. A typical filter does not allow contaminants to be removed from the fine media bed surface using the stock inlet nozzle without risk of loss of fine media due to backwash and fine media loss into the flow. Use of such a stock inlet nozzle is beneficial at the beginning of a backwash cycle. Additionally or alternatively, such a stock inlet nozzle is useful for use after an air flow backwash that causes contaminants to enter the liquid level above the media bed.

The present disclosure will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.
1 is a schematic diagram illustrating a configuration of a media bed filter in a filtration tank according to a typical prior art. FIG. 1 is a schematic diagram illustrating the configuration of a media bed filter in a filtration tank having trapped particulates and a cake-like crust on top of the media bed, according to a typical prior art. FIG. FIG. 6 is a schematic diagram showing a liquid backwashing operation using a gentle water flow in a filtration tank, having a sand filtration media bed, according to the prior art. FIG. 3 is a schematic diagram showing a backwash operation using a flow of air with a sand filtration media bed according to the prior art. FIG. 2 is a schematic diagram illustrating an embodiment in which a media bed filter is introduced into a filtration tank having a fine media layer on top of a media bed having trapped particulates and a cake-like crust on top of the media after filter operation. FIG. 2 is a schematic diagram illustrating one embodiment of an improved backwash process, showing contaminant wakes from fine media, with limited airflow resulting in a very narrow area and media bed in the water layer. It will bring about a fine media cloud that occupies only the top of the cloud. It is a schematic diagram showing a nozzle base liquid skimmer and a baffle base liquid skimmer for skimming a cake-like crust deposited on the top of the media bed. FIG. 6 is a partial perspective view of one embodiment of a media bed filter unit comprising a horizontal cylindrical tank with four nozzles and baffles for liquid inlets, a bottom cylindrical screen for filtered liquid outlets and backwash inlets. In FIG. 8, the filtration media is not clearly shown.

  FIG. 1 shows a typical arrangement of sand media in a multi-layer media bed filter placed in a tank 100. The media bed has a variety of densities as is known in the art. In such filters, typically the finest particulate medium 110 is disposed in the uppermost layer and comprises one or more intermediate stages 112 that become coarser as they descend through the various layers arranged vertically in the tank 100. . Thus, the coarsest grain medium 114 is typically placed in the bottom layer supported by the screen. In some cases, media 114 is placed at the bottom of tank 100 and a screen is associated with outlet 120.

  The precise definition of the fine, medium and coarse media in each of the various layers used in the present invention will vary depending on a variety of factors including, but not limited to, the field of practice, industry, usage conditions and government regulations. I want you to understand. However, for content comparison, one or more physical properties, such as media density or media diameter, may be a property choice for distinguishing the various layers of media in tank 100. For example, gravel or sand having a density of 2.7 g / ml is preferably placed in the coarsest bottom layer, activated carbon having a density of 2.0 g / ml to 2.1 g / ml is placed in the middle layer, and 1.45 g / ml. Anthracite with a density of ml to 1.75 g / ml is preferably placed in the finest top layer. Additional possibilities and features of the material are further described below.

<Basic arrangement and operating principle of media>
Typically, each independent layer of diverse media due to the granular texture characteristics of the sand is not placed within or delineated within a boundary that is finely defined by a particular boundary. The distribution of media with various particle sizes in the tank 100 is rough and typically varies gradually from the top to the bottom of each layer. In addition to the effects of changes due to filtration and other potential actions, the range of particle size, density and media roughness within each layer, diversity and tolerance, density, media, unless it is a potentially distinguishable layer Due to the effects of roughness, achieving full stratification of the media layer by particle size is generally considered more difficult in some embodiments. Thus, the various layers of the media can be separated by imperfect boundaries often found in the shape of the intermediate tapered region. However, even non-ideal arrangement of sand particle sizes, imperfect stratification, can prevent unintentional loss of sand media during the filtering operation or at any other time.

  After introducing various sizes of sand into the tank 100, rough stratification can be achieved by causing the normal fluid flow in the tank 100 to flow backward. By performing such an operation, smaller sand particles are floated, and subsequently the finer medium 110 floats at the top of the tank and the coarser medium 114 settles at the bottom. The resulting granular media 110, which is finer and does not interfere with the operation of the fine screen 116, which is placed in the top of the sand and in the mixed water, will be described in further detail.

  The more finely divided medium 110 acts to trap very fine particulate deposits, and the successive coarser layers 112, 114 are flushed from the tank 100 with the filtered liquid of the finer layer 110. Or alternatively, the formation of obstructions that prevent the filtered liquid from passing through the very fine screen 116. The role of sand media to mechanically absorb particulates is known in the art and will only be described schematically herein. This sand medium plays a role similar to the screen 116 that prevents the area immediately above the filtrate outlet 120 from becoming clogged, and gradually and continuously as the fluid flows into the screen 116, the medium 110, 112, Increase the porosity of 114.

  The stock solution to be filtered is introduced into the tank 100 through the stock solution inlet 118. Stock solutions can be introduced from any source. Its characteristics will vary depending on the environment in which the filtration tank is located and the particular filtration object. Therefore, the stock solution inlet 118 does not necessarily include raw sewage, but may be composed of industrial water used for cleaning purposes in industrial processes, for example. Alternatively, cooling water containing dust and traces of microorganisms can be introduced from the HVAC system.

  Deposited contaminants, particularly those that exceed the roughness of the particulate media 110, are trapped by the particulate media 110 on or at the media bed surface as shown in FIG. It can be prevented from moving. Cake or crust 102 may be formed on the surface of medium 110. Other contaminants that are similar or comparable in size to the particles in the layer of the particulate media 110 may penetrate the layer or travel a certain distance through the media layer with the upper layer 100 before the crust 102 solidifies. It is captured or captured as the fine particle 104 within. Contaminants that are not trapped in the first layer are likely not trapped in any subsequent layer with a continuous, coarser medium.

  Filters that are essentially similar to the structure described above are specific unless efficient operation is hindered by the deposition of contaminants such as aggregates of trapped particulates 104 within a crust 102 or fine media 110 layer formed on a media bed. Can operate according to a schedule or a specific period of time. By continuing to flow the stock solution 118 into the filter, trapped contaminants will accumulate in excess, resulting in generally inefficient operation and inefficiency. Backwashing, known as a filter maintenance process, is typically used when operation is inhibited as described above. Such a situation can be detected using a drop in pressure in the filter, and these pressures increase with the accumulation of contaminants.

<Conventional liquid backwashing in a conventional sand filter>
As described above, reversing the normal fluid flow within the tank 100 is useful for achieving stratification (or re-stratification) of various sand (or other particulate material) media. In certain configurations, this can be achieved by a backwash process. Backwashing involves flowing the cleaning liquid from the outlet side of the screen (inlet 152) through the media to the backwash outlet 154. Although the sediment on the top of the medium can be easily removed by the gentle flow 122, the removal function of the trapped sediment in the fine medium is limited by the gentle flow. The media typically requires “cleaning”, which is a mechanical operation with or without additives that aid in the removal of contaminants. One type of such operation is to provide a liquid flow that causes the medium to enter the partial suspension. This eliminates the need for mechanical stirring.

  In a conventional backwash operation, a less gradual flow can be used.

  By reversing the fluid flow during a typical filtration operation by more powerful means 124, the media can be temporarily lifted from its normal position and configuration.

  Countercurrent washing should be performed at a flow rate 124 sufficient to add kinetic energy to the medium, so that the medium is in a mixture of sand and water, as well as a coarser medium 112, in which the finest medium 110 is continuous. When suspended on 114, complete suspension cannot be achieved. The flow rate described above should be configured so that the finest medium 110 does not flow out or is lost as part of the sand water flowing out through the backwash outlet.

<Conventional air flow backwash in a conventional sand filter>
A related backwash process known in the art includes countercurrent cleaning with air and liquid (see FIG. 4). In addition, in some sand filter configurations, a liquid backwash and air backwash process is applied. In these two backwash configurations, typically two types of backwash will not be applied simultaneously.

  During normal filtration operations, the tank 100 is typically filled with the liquid to be filtered, as well as a variety of sand media that are roughly layered according to the configuration described above and are layered continuously. The air backwash is performed after the filter operation is first interrupted. Subsequently, the liquid level in the tank 100 is typically lowered by allowing the liquid to flow out through the filtered liquid outlet 120. A level sensor is used to detect when the amount of water in the tank 100 falls below a target allowable height. The liquid level reduction described above can be similarly performed by introducing a large amount of air through the inlet / outlet 160 to form a cavity 162 in the tank 100 and extruding a corresponding amount of liquid. . Air can be introduced from any suitable source, such as a pump or air compressor. Once the air cavity 162 is formed and the associated fluid level in the tank 100 has dropped to a sufficient level, unwanted opening inlets and outlets (including but not limited to the filtered liquid outlet 120) are provisionally sealed. Then, cleaning of the sand medium itself starts.

  To clean the sand media, the air stream 126 is introduced into the tank in a configuration that causes sand mixing similar to the turbulent flow cycle or liquid backwash described above. Similarly, such a turbulent flow reproduces a suspended state by liquid backwashing without causing a risk of causing the medium to flow out of the tank 100. For this purpose, backwash fluid, typically air, in this case, is introduced through the backflow fluid inlet 152 to quickly diffuse the bubbles 170. The applied air flow uses inexpensive and efficient mechanical means for stirring the medium. For mixing the medium using air introduced through the backwash fluid inlet 152, a stirrer similar to a stirrer used in a washing machine for clothes is used. In addition, air circulation is advantageously used to randomize sand media of different particle sizes and densities, thereby reducing costs and adding additional costs, for example when stirring through mechanical arms or motorized paddles. It is possible to maximize the state without obstruction and blocking of access to the tank 100, while reducing the physical drawbacks of the mechanical parts, additional barriers to accessibility.

  Although not shown in FIG. 4, most of the fine medium 110 and the intermediate medium 112 are homogenized by the air backwashing operation. In some cases, the coarse media can be suspended. As will be described later, the homogenized medium can be separated or hierarchized using a liquid backwashing process, whereby the medium can be hierarchized.

<Detergent / Chemical detergent to assist cleaning>
In some backwashing means known in the art, agglomeration is initiated, utilized and used simultaneously with a detergent and / or clarifier during the backwashing process, regardless of whether the means using liquid or air is handled. Can be promoted.

  In a manner similar to using soap during washing, the operator can select a preferred detergent in addition to the use of various backwashing means. Soap removes oil and dirt from garment fibers, and flocculants or surfactants remove agglomerates, or remove particles and contaminants resulting from sand particles due to turbulence during the liquid or air agitation process described above.

<Liquid backwash after air backwash>
When the air backwashing is completed, the homogenized medium in the tank 100 is mixed again, and the rough hierarchization according to the roughness as described above and the hierarchization required for the filter operation are largely lacking. . Liquid backwashing (or other means of layering media) can be used after air backwashing to ensure restratification of sand media of various sizes. As described above, the counter flow for subsequent liquid backwashing can be adjusted to ensure re-stratification and sand media inclusion based on propulsion. On the other hand, a flow rate that is strong enough to hold a coarser sand medium at a low position in the media bed while placing a smaller sand medium at a high position in the tank 100 must be properly selected. On the other hand, the flow rate must be strong enough to prevent all sand media from unintentionally flowing out of the tank 100.

<Fine media>
Sand media particles can be stratified in the same manner as other earth and sand materials, with dimensions within specific ranges based on various requirements. The above-mentioned requirements, which are defined in a non-limiting manner, can be considered as one of the functions of the technical field, government regulation and / or implementation field. Fine sand is a subordinate concept of sand and the size of the media particles will fall under the subordinate concept. Thus, fine sand (as shown in FIG. 7) can be used to advantageously apply a finer filter layer 128 in the media bed, allowing the capture of particulates having small dimensions. It is now possible to capture a group of contaminants that were previously impossible to filter, such as living microorganisms, and in some cases, could make previously drinkable water drinkable. it can. There is no single exact technical definition for “fine sand”, but “fine media”, as defined above, is effective less than 0.4 mm, at least about 0.2 mm, preferably at least 0.1 mm. It means a fine filtration medium having a diameter, and the material may be silica sand, glass, plastic, quartz, gravel, metal, ceramic and the like. The term “fine sand” will be understood to refer to any filtered sand or particulate media that is known in the art and has a better dimension and filtration function than the finest particulate media that has been used. . The range and configuration of possible dimensions for such media may be selected from those detailed and expressed herein.

<Disadvantages of fine media>
Unfortunately, there are also disadvantages to applying the finest filtration layer using fine media (eg, on the top layer of the filter). Smaller pore sizes typically can adversely affect the operation and maintenance of existing filtration systems.

<Problem: Precocious crust formation in fine media>
As the pore size of the top layer of the media bed is reduced, for example, a strong pressure will need to be applied to the stock solution passing through the filtration tank containing the fine media. In addition, more contaminants will be trapped in the top layer comprising fine media 128 or a portion thereof than prior art systems where the finest layer comprises a relatively coarse media. Thus, more contaminants are often trapped within a certain time or rapidly impedes the flow of stock solution through the filtration system. Preventing crust formation and contaminant deposition in a portion of the top layer is operationally important. As crust 202 (see FIG. 5) and microparticles 204 are formed, the porosity initially provided by the use of fine media is rapidly reduced, and rising pressure (which may hinder operation) continues. Required for dynamic operation. Therefore, the finest media may have a much worse filtration performance than the coarser conventional filtration systems. Therefore, the fine media filter needs to be backwashed with a shorter cycle than when a normal sand bed filter is used.

<Problem: Backwashing of fine media> Due to the finer fine media, the corresponding range of sand that can be suspended much more easily than the corresponding larger particles for the conventional liquid backwash described above Particles can be introduced. As a result, the fluid flow tolerances at the inlets 118, 152 need to be adjusted more carefully. Additionally, the operator and operator (or automated operating system) can reverse the backwash fluid outlet 154 without draining sand (a slurry composed of sand and mixed water similar to conventional sand particles 105). A flow of sufficient strength to achieve sand media suspension at the wash fluid inlet 152 must be provided. In this case, the backwash inlet 152 fluid volume range, which is generally more limited (and inferior in volume and performance), applies to filtration systems that do not have a fine media layer. A fluid inlet flow that can be used at a lower flow rate prevents proper cleaning of the sand media by the operator performing maintenance. Thus, while the acceptable flow rates used in conventional sand allow for the acceptable level of cleaning that class of filtration systems should achieve, the extremely low flow rates that are acceptable when fine media are present as filtration media are mostly In this case, imposing such constraints makes these media almost useless. Even when a significantly lower back flow rate is used at the inlet 152, smaller fine media can easily flow away from the tank 100, so a lower range of flow rates is acceptable. For example, if all kinds of sand existing in the tank 100 are mixed, and the cleaning power of the sand medium in the backwashing process is reduced, an influence of disturbing mixing may occur.

  Even after re-stratification, sand media that settled after backwashing (with a backwash flow rate low enough not to wash away sand particles of fine sand within the range) were treated in the previous process. A certain amount of contaminants present in the stock solution remains. Incorporating fine media having a cleaning function due to porosity into the media bed, ironically, can result in a reduction in the overall function of the filtration system.

  Additionally, the media bed cannot be effectively cleaned by backwashing with liquid alone, especially in fine media. In the first test, the applicant used a tank with a fine medium having the finest filtration layer. In addition to performing two 10 minute backwash cycles (including a filtration cycle that cleans to ensure that no residue remains in the system), Applicant demonstrates the cleaning of the media as a result of the cleaning process. It was observed that the washing water had a maximum turbidity of 5 nefero analysis turbidity unit (NTU). Analysis of the surface medium indicated that kaolin was trapped in the medium and that cleaning was not effective. Further observation results will be described later.

  As in the case of the backwashing process of the fine medium with the liquid, applying the conventional backwashing process with air to the filtration system in which the fine medium is the filtration medium is problematic and hindered by physical concerns. .

  Conventional air backwash has the problem of collecting a slurry of wet sand particles 105 and contaminated wash water 140. When the generation of bubbles stops, the sand (or medium) becomes calm. Thereafter, the contaminated water can be discharged by introducing clean water through the backwash fluid inlet 152.

  When the fine media 128 is present in the filtration media, the slurry settles at a significantly slower rate than when no fine media is present, so the fine media requires a relatively long time to settle. More importantly, the air wash homogenizes the fine media with the coarser support medium and the fine media after the air wash remains mixed with the coarser media. This can cause the fine medium to flow to the lower support medium and / or the outlet and be lost. For this reason, destruction of hierarchies is required. As mentioned above, the stratification breakdown of fine media and lower support media is a problem. Furthermore, in the calming process in the presence of a fine medium, as the calming occurs, more contaminants are condensed in the uppermost layer. Therefore, normal air backwashing is also difficult to operate in the presence of fine media. The improved backwash process is believed to be as follows. That is, it effectively separates contaminants from the filtration medium while providing sufficient effects due to the strength and turbulence of the bubbles without unnecessarily stirring the filtration medium.

<Solution by fine media backwash>
The solution proposed by the Applicant uses a fine medium having a density lower than the density of the finest particle size at least next to the finest particle size in the filtration media bed, as shown in FIG. The liquid flow rate used for normal filtration media bed stratification is simply too large for fine media. Applicants have noted that the media layer has been stratified even during backwashing as long as the density of the media increases with particle size to aid stratification and the air flow rate is controlled to prevent mixing. I found it possible to keep the state. During such air backwashing, the lower layer of the medium is not disturbed, and the fine medium can remain in the upper suspension of the lower layer. It can also be combined with a lower level liquid backwash as long as the fine media does not flow out of the reservoir due to the liquid flow. The denser media continues to assist in separating the fine media from media with larger particle sizes during the stratification process, thus preventing the fine media from being captured by other media. When air backwashing and liquid backwashing are stopped, the fine media is placed on top of the remaining layered media.

In some embodiments, the air flow rate typically ranges from 40 m ³ / m ² / h to 55 m ³ / m ² / h, for example, 0.15 mm fine sand is 55 m ³ / m ^2. A flow rate of / h is appropriate, for example when mixing large filtration media with a particular configuration with larger particles or higher sticky particulates, even up to 60 m ³ / m ² / h is desirable . Air can be injected through the fluid inlet 152 or other inlet. Air flow control means (not shown) can be provided to set the desired air flow, for example to control the air flow using a float flow meter, mass flow meter or pitot tube velocimeter. it can. Air distribution can be performed using a screen 116 or other diffuser (not shown). Air flow using a diffuser produces bubbles (which produce bubbles that move in the media bed), which causes the fine media to reach level 220, which is a relatively high height above the media bed. Mixed with a liquid (clean water) layer 225. The fine media is homogenized with the fine media 110 and possible intermediate media 112 when the air flow is high.

  However, the media 110 and 112 remain in a layered state while the fine media 128 is suspended in the aqueous layer 225. As noted above, a small amount of liquid flow (eg, raising the level 220 to tentatively approach the outlet 154) can be used to continue separating the fine media cloud 240 and fine media 128 from the fine media 110. it can.

  As the bubbles 170 are pushed up into the water layer 225 in the tank 100, the countercurrent of the water flow flows downward without causing the strong through flow seen in conventional air backwashing. Such action activates the overall flow alternating current, and contaminants gradually flow upward from the media bed 226 and are collected in the water layer 225 between the fluid level 220 and the media bed top. By the action of the bubbles 170, the mixture is adhered or trapped between the fine media pushed up into the water layer 225. As a result of this alternating current, contaminants are collected in the water layer 225, but are not captured again in the fine media layer of the media bed when the air supply is stopped. Instead, if it is determined that the contents of the media bed are clean, the contaminated contents mixed in the aqueous layer 225 are gently drained. This flow rate is insignificant, but the overall stratification desired for the filter is ensured by ensuring that the spillage is slow enough not to disturb the top (fine media) layer 128 of the media bed. This is important because it can be configured so as not to disturb. Alternatively, after re-stratification, the collection of contaminants in the water layer 225 can be done from the top of the media, i.e., through the inlet, for example using purified stock inlet nozzle 250 (see Fig. 7) This is possible by pouring and letting out contaminated water through the outlet 154.

  By using a lower density fine medium in the uppermost layer of the medium bed and making the larger continuous particles higher in density, it is possible to prevent the layering from being destroyed as the end of air backwashing approaches. . The bubbles 170 and the flow they generate do not disturb the media bed layer or cause stratification breakdown.

  Thus, with air backwash cleaning, the coarsest bottom support medium moves only slightly, but disrupts the fine media 128 and the coarser media (fine grain media 110) that support the fine media, resulting in homogenization. In order to avoid significant disturbance of the medium, after the air backwashing, the fine medium is separated from the upper part of the coarser medium, and the fine medium is arranged on the upper part. This can be achieved primarily by choosing to apply a higher density to the coarse support medium than to the fine medium. Adding a low level of liquid backflow at the end of the air wash can assist in separating the fine media from the coarser support media during the calming process. This reverse flow can avoid the risk of the fine medium flowing away through the top of the filter. Further, the air flow in the backwashing can be reduced, so that the fine particle medium 110 can be calmed down while maintaining the suspended state of the fine medium 128 above the fine particle medium 110. When the air flow is blocked, mixing of the fine medium 128 and the fine particle medium 128 does not occur. Therefore, re-hierarchization can be avoided without causing the fine medium to flow out.

Each table shows the values that various media layers in some embodiments may have.

Immediately after the first test described above, the second test was performed, and the applicant performed a backwash by airflow. This test was conducted at an industrial site in South Dakota, USA, using a filter with a performance of 68 m ³ / h (300 gallons per minute). The factory needed good quality water to supply the reverse osmosis membrane (RO) system. The factory used an ultrafiltration (UF) membrane in front of the RO system. The UF membrane was contaminated very quickly and could not be purified to regenerate the source. For this reason, the fine sand filter is used to improve the filterability of water and remove some turbid substances that reach the UF membrane by performing pretreatment of water before reaching the UF membrane.

  Two water sources are used, a first water source having a turbidity of about 15-30 NTU supplied from the lake and a second water source having a turbidity of about 100 NTU (up to 300 NTU) supplied from the pond. It was measured. Since this pond has drainage from the plant, it can be reused to improve the water balance of the plant.

Since the influent concentrate was solid, the filter was used at about 200 gpm (45 m ³ / h) to optimize the filter removal function.

  The filter is activated and the suspension concentrate causes many of the water-only backwashes to occur about once every two hours. After 2 weeks of operation, the 4 psi media differential pressure could not be maintained. In practice, the filter media was contaminated and could not be purified after many successive backwashes of water. In this test, a maximum turbidity of 230 NTU was observed. This indicates that many contaminants were present in the sand but were not collected after the first backwash.

  Subsequently, a pre-backwash air wash was activated, and after only 2 backwashes, the filter can recover to a fully cleaned state with a media differential pressure of 4 psi at 200 gpm. The filter operates continuously for about 12 weeks, always with a high load of organic suspension, and can always recover to full operation at a clean filtration differential pressure of 4 psi.

  In further tests, raw water with a turbidity of 11.19 NTU (light yellow) was analyzed using a Spectrex laser particle counter and had an average particle size of 2.98 micrometers (standard deviation 2.51 micrometers). The total particle amount was found to be 93,947 / ml. Fine particle filter outlet has 1.98 NTU (mostly clean), average particle size (standard deviation 2.03 micrometers) is 2.35 micrometers, and the actual total particle volume is 27,155 / ml I understood.

  With the introduction of the filter in this test, the filter pressure before the start of backwashing dropped to 17 psi. Prior to backwashing, the NTU difference was about 12 NTU, after the air backwashing described above, the pressure dropped to 6 psi and the NTU difference increased to about 13 NTU. In this test, the differential pressure reached 20 psi, the NTU difference reached 21.4 NTU-2.4 NTU = 19 NTU, and after backwashing with air, the differential pressure was 5 psi and the NTU difference was 21.3 NTU-0.7 NTU = 20.6 Repeated when reaching NTU. In this test, the differential pressure reached 20 psi and the NTU difference reached 17.8 NTU-2.4 NTU = 15.4 NTU.After air backwash, the differential pressure was 4 psi and the NTU difference was 17.8 NTU-1.1 NTU = 16.7. Repeated when reaching NTU.

  Fine particle air backwashing without interfering with stratification makes it possible to quickly remove contaminants from the fine media, thus reducing downtime of the filter during operation. Since fine media is more effective at trapping contaminants with dimensions of 0.5 to 20 microns, more frequent filter cleaning is required to maintain filtration efficiency, and thus Frequent cleaning can be facilitated by air backwashing media having a composition with a density that allows air backwashing without destroying the layering of the filter media bed.

<Outflow of contaminated water after backwashing>
The contaminated water can usually be drained by introducing clean water into the tank 100 through the filter floor. In order to prevent the fine medium from being suspended or washed away, the flow rate with the fine medium must be set very low. Thus, additional inlets can be used on the filter media. If the fine medium is not disturbed by the flow, the stock solution inlet 118 can be used. Similarly, by introducing clean water with a moderate flow rate that is very gentle to avoid cloud formation (of fine media 240 or any media bed contents) into the tank through backwash inlet 152, Can be started. Similarly, the appropriate flow rate varies slightly, a portion of which is determined by the diameter of the finest layer present in the media bed. For example, in the case of a fine medium having a diameter of 0.15 mm, a flow rate of 15 m ³ / m ² / h can be applied. The flow rate can be slightly reduced, for example, for glass beads having a diameter of 0.2 mm, a flow rate of 13 m ³ / m ² / h can be applied. In the case of slightly larger diameters, for example glass beads having a diameter of 0.3 mm and plastic particles having a diameter of 0.6 mm, a flow rate of 25 m ³ / m ² / h can be tolerated. Directing clean water from either of the inlets 118, 152 to the surface of the media bed is an important first step, after which water is drained.

  In another embodiment (FIG. 7), the surface-directed nozzle 250 is directed to drain water through the baffle 251 and flushes the contaminated water with contaminants, particularly large particles, covering the top surface of the media bed. Can be provided. The use of one or more nozzles 250 in this manner with a baffle for backwashing cleans the top layer of the media bed without unintentionally draining large amounts of sand from the tank 100. Is particularly effective. The baffle design allows a stream of skimming to flow on the surface of the media floor.

In operation, the liquid skimmer using the nozzle 250 and baffle 251 described above can typically be activated prior to performing any other cleaning operations. Actuating in this way has the advantage that crusts 102, 202 or particulates 104, 204 can be collected at the top of the media bed. Collecting top-level contaminants in the media maintenance process before other work steps, so that in any subsequent backwash process, the presence (or trapped) of contaminants at the top of the fine media It can be eliminated significantly and advantageously. Further, such a method can effectively disperse contaminants from the top of the media bed without simultaneously causing excessive agitation or turbulence in the fine media with the media bed top. When the normal flow rate of the filter in normal operation reaches 136 m ³ / h (600 gpm), the flow rate from the baffle will be about half of the filter flow rate, up to about 68 m ³ / h (300 gpm). Can be.

  Additionally, the use of baffles is known in the art as a better improvement than using a mechanical stirrer. The stirrer requires additional mechanical parts with special complexity and has additional concerns, whereas the operation of the baffle is advantageous because it uses the physical infrastructure already used in the filtration process. It is. Not having additional moving parts that are compatible with existing hardware is further advantageous in quality and effectively improves the disadvantages of conventional liquid backwashing.

  A particular advantage of the solution described herein is the possibility and advantage of avoiding frequent use of cleaning agents. Typically, backwashing requires a time scale that is measured based on minutes, hours, and days, and if not reduced to a single use over a period of months, a surfactant or flocculant. The need to add can be eliminated. Although the configuration of a particular filtration system varies widely, the use of detergents is typically necessary if the operator believes that the backwash method described herein is not effective and / or Only in rare cases, such as when there is a real need to use and wash sand. A rarer case is when it is necessary to reconstruct the entire contents of the media floor.

  The description of FIGS. 1-7 relates to any desired tank 100 shape. FIG. 8 shows a cross-sectional view of a horizontal columnar embodiment. Such a configuration shows a large medium surface in a compact configuration. The liquid inlet 118 enters through a side port on the upper surface of the tank via a T-joint and feeds a plenum with four nozzles that transfer the stock solution to the baffle 251. Any suitable configuration for supplying the stock solution to the tank can be used. In this embodiment, by providing the fine medium in the vicinity of the baffle 251, the filtration function of the fine medium can be improved by the stock solution flow. For example, the medium can comprise three types of media, with the finest medium at the top, the medium with intermediate particle size in the middle and the coarsest medium at the bottom. The screen 116 is a cylindrical tube of mesh material that communicates with the discharge port 120. Since the screen 116 can be closed at the top and opened at the bottom, the filtrate can be collected from the bottom of the media. On the side of the screen 116 is provided an air conduit 152 'that generates bubbles at the screen level in the coarse-grained medium. An air conduit 152 'can be provided near the boundary between the coarse and intermediate media when surrounding the screen 116 and the media has three stages. In this way, the filtrate discharge can be decoupled from the air transfer, but in some cases the air can also be injected for backwashing in the screen 116. The lower medium can assist in the distribution of bubbles that originate from the air conduit 152 'towards the medium and the fine medium. As described above, air backwashing does not cause mixing of the fine and coarse media so that media re-hierarchy is required.

Claims (14)

A media floor filter,
A reservoir having a stock solution inlet and a filtrate outlet;
By including an upper layer of a fine medium comprising a lower layer granular material having an increased density and particle size, the fine medium can be produced without the occurrence of layered structural destruction of the fine medium and the need for re-hierarchization of the hierarchical medium. Layered filtration media of various sizes with granular materials of various densities that allow air backwashing of the media;
Backwash air distribution means for injecting air through the filtration medium;
A media bed filter comprising a backwash drain and an air valve.   The filter of claim 1, wherein the fine medium comprises sand particles.   The filter of claim 1, wherein the fine medium comprises glass particles.   The filter of claim 1, wherein the fine media comprises polymer particles.   The apparatus further comprises a backwash air flow control unit adjustable for setting a backwash air flow rate that is efficient for cleaning the fine medium without destroying the hierarchical structure of the fine medium. The filter according to any one of 4.   6. The filter of claim 5, wherein the fine medium has a density that is at least 1 g / ml lower than the density of the underlying granular material.   The bottom layer of the hierarchical medium comprises a granular material having a diameter in the range of 2.5 mm to 6 mm, and the intermediate layer of the granular material comprises a granular material having a diameter in the range of 0.5 mm to 2 mm. 7. A filter according to claim 6, wherein the upper layer comprises a granular material having an effective diameter in the range of 0.1 mm to 0.4 mm, preferably 0.1 mm to 0.2 mm.   The intermediate layer has a density of about 4 g / ml and the upper layer has a density of less than 3 g / ml, preferably these layers are sand material having a density of about 2.7 g / ml, about 2.5 g 8. A filter according to claim 7, comprising a glass material having a density of / ml or a plastic material having a density of about 1.6 g / ml.   The filter according to any one of claims 6 to 8, wherein the bottom layer includes garnet particles.   The filter according to any one of claims 1 to 9, wherein the backwash air distribution means comprises a conduit surrounding the filtrate outlet screen.   The filter according to any one of claims 1 to 10, further comprising controlled backwash air supply means.   Control means for automatically controlling the valve to cause an air backwash cycle in the fine medium is further provided. By this cycle, the fine medium and the dispersion of the fine medium are mixed with a large amount of washing water. 12. A filter according to claim 11, wherein the fine medium is localized in the lower part of the wash water so that it is not contained in the upper part of the wash water during the air backwash.   The stock solution inlet has a stock solution distribution nozzle configured to direct a flow from the stock solution inlet to a main portion of the surface of the filtration medium, and a controllable connection to the stock solution distribution nozzle so that deposits pass through the backwash drain. The filter according to claim 1, further comprising a backwash fluid inlet for flowing out the deposit on the surface of the filtration medium without dispersing the fine medium to remove water. A media floor filter,
A reservoir having a stock solution inlet and a filtrate outlet;
A filtration medium including a fine medium;
A stock distribution nozzle configured to direct flow from a stock solution inlet to a major portion of the filtration media surface;
Backwash drain,
A backwash fluid inlet,
The backwash fluid inlet is controllably connected to the stock distribution nozzle to flush out the deposit on the surface of the filtration media without dispersing the fine media to remove the deposit through the backwash drain. A media floor filter characterized by the above.